As is noted in U.S. Pat. No. 4,998,763 granted on Mar. 12, 1991, to Henke, there is a need for cargo hooks which can not only secure and carry a load, but which can also quickly and reliably release a load if the need arises. This is particularly so in the case of helicopter logging or similar airborne operations where substantial loads may be lifted and carried beneath helicopters. Typically, a cargo hook will be secured at one end of a long cable (60 to 100 meters, for example), the other end of the cable being secured to the helicopter. In the case of logging operations where the cargo hook may be referred to as a logging hook, several logs collectively weighing several thousand kilograms (3000 to 5000 kg., for example) will in turn be secured to the hook, each by a relatively short length cable (6 to 9 meters, for example).
In the event of a flight emergency, the ability of a cargo hook to rapidly and reliably drop or release a load is obviously critical for the purpose of flight safety. In addition, however, there are certain types of operations where the ability to drop or release a load while the hook is under load may be a standard part of the operation. For example, and again in the case of helicopter logging operations, it is not unusual for a helicopter to be called upon to transport logs from logging site to a location above water where they are deliberately dropped for subsequent recovery and collection in log booms or on boats or scows.
As another example, it will be noted that a pair of cargo hooks may be used in some helicopter logging operations. In such cases, a rigger on the ground will load up the pair of hooks while the helicopter hovers above. The rigger will make an educated guess as to the total weight of the logs but, on occasion, the load may be too heavy for the helicopter to comfortably lift. Not to delay and slacken the load while the rigger removes some logs, the helicopter pilot may prefer to simply release the load carried by one of the hooks and carry off with the load which remains on the other hook. Typically, the pair of cargo hooks used in such operations will be two separately housed hooks mounted on a single frame.
Various cargo hooks have been used for helicopter logging operations. However, the mechanisms for load release are generally subject to very high loads with resulting wear and tear after repeated usage. In the case of the above noted patent to Henke, a design is described which limits the transmission of load forces to the release mechanism. However, particularly in the case of a heavy load such as that presented by a collection of heavy logs, the transmitted forces can remain quite significant in relation to the material strength of components used in the design. Even though the components used in the release mechanism of the Henke design are advantageously limited to components which are in abutment or rolling contact, the high forces which are at play can lead to the development of flat spots which can detract from the smoothness of release and ultimately limit the useful lifetime of the hook.
A primary object of the present invention is to provide a new and improved cargo hook for releasably carrying a load, and which may be structured so as to transmit a minimal amount of the loading force to the release mechanism.
A further object of the present invention is to provide a new and improved cargo hook which is particularly adaptable for carrying heavy loads as in helicopter logging operations.